Recently, a study was carried out to determine who was the greatest American president. Sixty­five presidential historians took part in it, and they judged the past forty­four American leaders based on ten leadership qualities, including public persuasiveness(信服), crisis leadership, management of the economy, moral leadership, and conduct of international relations. The historians also looked at administrative ability(管理能力), relations with Congress, ability to set goals, and the pursuit of equal justice for all. Finally, the experts took into consideration the historical period in which the president lived.

       The historians chose Abraham Lincoln as American's greatest president. He had also been named the greatest president in a similar study in 2000. Abraham Lincoln was the president who led the nation through the Civil War in the 1860s, and was able to unite it in the end. He also took the first steps to abolish(废除) slavery in America.

       Edna Medford, a professor of history at Howard University in Washington, D．C., was an adviser on this study and the earlier one. She says Abraham Lincoln is seen to represent the values the nation most honours, such as truthfulness, moderation, and respect for human rights.

       The historians put American's first president, George Washington, second on the list, while Franklin D. Roosevelt, Theodore Roosevelt, and Harry S. Truman follow in that order. John F. Kennedy, the country's first Roman Catholic president, is sixth on the list. Like Lincoln, Kennedy was murdered while in office.

       Among recent presidents, Ronald Reagan was named the tenth best and Bill Clinton rated fifteenth, while the historians put former president George W. Bush at number thirty­six. His father, George H．W. Bush, did much better, being placed at number eighteen.

如图，等边三角形ABC中，点D，E分别为AB，AC的中点，则∠DEC的度数为（　　）

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